1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to a valve useable undersea and connected to a low pressure recipient and related methods, more particularly, to a valve useable in an apparatus for operating a deep-sea blowup preventer (BOP) by generating a force due to a pressure difference between the hydrostatic pressure and a substantially lower pressure.
2. Discussion of the Background
During the past years, with the increase in price of fossil fuels, the interest in developing offshore drilling has dramatically increased, since offshore locations appear to hold vast amounts fossil fuel.
A typical offshore drilling system 10 is illustrated in FIG. 1. The system 10 may include a vessel 12 having a reel 14 (e.g., a Mux Reel) that supplies power and/or communication cords 16 to a controller 18. Some systems have hose reels to transmit fluid under pressure or hard pipe (rigid conduit) to transmit the fluid under pressure or both. Other systems may have a hose with communication or lines (pilot) to supply and operate functions subsea. However, a common feature of these systems is their limited operation depth. The controller 18 is disposed undersea, close to or on the seabed 20. In this context, it is noted that the elements illustrated in FIG. 1 are not drawn to scale and no dimensions should be inferred from FIG. 1.
A wellhead 22 covers a subsea well 23 and a drill line 24 enters the subsea well 23. At the end of the drill line 24 may be a drill (not shown). Various mechanisms, also not shown, may be employed to transmit rotation via the drill line 24 to the drill in order to extend the subsea well deeper in the formation under the seabed.
During normal operation of the system 10, unexpected high pressure flow of gas, oil or other well fluids (the high pressure exceeding the pressure of drilling fluid in the drill line 24) may emerge from the formation into the well. This kind of unexpected event (sometimes referred to as a “kick” or a “blowout”) could damage the well and/or the equipment used for drilling.
In order to prevent the damaging effect of this kind of events, a pressure controlling device, for example, a blowout preventer (BOP), is usually installed on top of the well 23. The BOP is conventionally implemented as a valve closing to prevent the release of the high pressure fluids emerging from the well either in the annular space between a casing and a drill line 24 or in the open hole (i.e., hole with no drill pipe) during drilling or exploitation operations, respectively. The controller 18 controls a system of valves (not shown) in order to provide the force necessary for opening and closing the BOPs 26 and 28.
Traditionally, the force necessary to operate the BOPs is generated due to a pressure difference between the hydraulic pressure and a pressurized hydraulic fluid. The hydraulic fluid used to generate this force is commonly pressurized by equipment on the surface. The pressurized fluid is stored in an accumulator (e.g., 30 in FIG. 1) that is lowered subsea, close to the location of the BOPs, after being charged. The accumulator 30 may include plural containers (canisters) that store the hydraulic fluid under pressure to provide the necessary pressure to operate (close and open) the BOPs. The high pressure hydraulic fluid may be selectively provided via the pipe 32. The generated force is transmitted to BOPs 26 and 28.
A conventional apparatus 40 for generating a force used to operate the BOPs is illustrated in FIG. 2. The accumulator 30 is connected via valve 34 to a cylinder 36. The cylinder 36 includes a piston (not shown) that moves when a pressure difference occurs between the volumes separated by the piston, thereby generating a force used to operate a BOP 27 (which is one of the BOPs 26 and 28). The force is generated due to a pressure difference occurring in the cylinder 36 when the controller 18 makes the valve 34 to open a fluid communication from the accumulator 30 to the cylinder 36.
As understood by those of ordinary skill in the art, in deep-sea drilling, in order to provide hydraulic fluid having a pressure larger than the hydrostatic pressure generated due to the seawater at the depth of operation of the BOPs (e.g., ˜240 atm at 2500 m depth), the accumulator 30 is initially charged at the surface. Typically the accumulators are charged with nitrogen. As the required pressure increases with the operating depth, the efficiency of storing the hydraulic fluid (e.g., nitrogen) useable deep-sea decreases, which adds additional cost and weight because more accumulators are then required to perform the same operation as on the surface. For example, an accumulator having a 60-liter (L) capacity and a useable volume of 24 L on the surface has a usable volume less than 4 L at 3000 m of water depth. Therefore, using accumulators to store high-pressure hydraulic fluids to operate a BOP makes the operation of the offshore rig expensive, and requires the manipulation of large parts. In other words, providing hydraulic fluid having a pressure larger than the hydraulic pressure deep undersea becomes prohibitively expensive. The equipment for charging, deploying and maintaining the accumulators is bulky, as the size of canisters that are part of the accumulator 30 increases. The range of operation of the BOPs is limited by the initial pressure difference between the charge pressure and the hydrostatic pressure at the depth of operation (i.e., deep-sea). With increasing depth (i.e., the distance from the sea surface to the seabed), storing high pressure hydraulic fluid in accumulators becomes less efficient, while the hydrostatic pressure increases, making it necessary to increase the size of the accumulators (e.g., it may become necessary to use 16 320-L bottles of nitrogen).
As disclosed in U.S. patent application Ser. No. 12/338,652 filed on Dec. 18, 2008, entitled “Subsea Force Generating Device and Method” to R. Gustafson, the entire disclosure of which is incorporated herein, an apparatus 50 as illustrated in FIG. 3, generates a subsea force F based on a pressure difference between the hydrostatic pressure and a pressure lower than the hydrostatic pressure.
The apparatus 50 includes an enclosure 52 having inside a piston 54 configured to move along thereof. The piston 54 divides the enclosure 52 into a chamber 56, called the closing chamber, and a chamber 58, called opening chamber, as shown in FIG. 3. A pressure difference between the opening chamber 58 and the closing chamber 56 yields an actuation force moving the piston and transmitted, for example, to a ram block (not shown) of the BOP via a rod 57.
When the BOP is not actuated (i.e., closed or opened), the pressure in both chambers 56 and 58 may be the same, e.g., the hydrostatic (ambient) pressure. Having fluid at ambient pressure (Pamb) in both chambers 56 and 58 may be achieved by allowing the sea water to freely enter these chambers via corresponding valves (not shown). Thus, when there is no pressure difference between the chambers 56 and 58 on opposite sides of the piston 54, the piston 54 is at rest and no force F is generated.
When a force becomes necessary (e.g., to close the BOP when and unexpected kick event occurs), a pressure imbalance may be created between the chambers 56 and 58, for example, by allowing a fluid communication between the opening chamber 58 and a low pressure recipient 60 via a valve 62. The pressure Pr inside the low pressure recipient 60 may be as low as 1 atm. The valve 62 may be switched between allowing or not the fluid communication between the opening chamber 58 and the low pressure recipient 60, by a controller connected to the valve via a line 63. While a valve (not shown) allowing sea water to enter the opening chamber 58 is closed before the fluid communication between the opening chamber 58 and the low pressure recipient 60 is established, the closing chamber 56 may continue to receive sea water at hydrostatic (ambient) pressure via a pipe 64. Thus, as the piston 54 moves towards right in FIG. 3, the volume of the closing chamber 56 increases but due to additional sea water the pressure remains the same, i.e., the hydrostatic pressure at the operating depth. After the fluid communication between the opening chamber 58 and the low pressure recipient 60 is established, the pressure in the opening chamber 58 decreases towards the low pressure Pr, while seawater from the opening chamber 58 may enter the low pressure recipient 60, until the pressures in the opening chamber 58 and the low pressure recipient 60 become equal.
Although the arrangement shown in FIG. 3 and described in patent application Ser. No. 12/338,652, to R. Gustafson discloses the manner of generating the undersea force without the use of the accumulators, in one embodiment discussed therein, the accumulators still may be used to supply a supplemental pressure to the closing chamber 56.
Thus, a pressure difference between the closing chamber 56 and the opening chamber 58 triggers the movement of the piston 54 to the right in FIG. 3, generating the force F. However, because the seawater from the opening chamber 58 is released into the low pressure recipient 60, the low pressure recipient 60 cannot again supply the same low pressure unless a mechanism is implemented to empty the low pressure recipient 60 of the received sea water. In other words, the seawater that partially occupies the low pressure recipient 60 after valve 62 has been opened, has to be removed and the gas at the low pressure that existed in the low pressure recipient 60 prior to opening the valve 62 has to be restored, for reusing the low pressure recipient 60.
The low pressure recipient 60 may be reset to its initial state by providing a reset recipient connected to the low pressure recipient 60, as described in U.S. patent application Ser. No. 12/338,669, filed on Dec. 18, 2008, entitled “Rechargeable Subsea Force Generating Device and Method” to R. Gustafson, the entire disclosure of which is incorporated herein.
Another way to reset the low pressure recipient at its initial conditions is described in U.S. patent application Ser. No. 12/960,770, filed on Dec. 6, 2010, entitled “Rechargeable Subsea Force Generating Device and Method” to R. Gustafson, the entire disclosure of which is incorporated herein. Therein, it is described that a pump may be connected to the low pressure recipient to remove the seawater or other fluid and reestablish a low pressure of a gas inside the low pressure recipient.
The valve 62 may be a dual chamber valve 70 as illustrated in FIG. 4. The valve 70 may have various ports 70a to 70e to allow connecting other various components to the valve 70 (i.e., to block or allow a fluid communication between a connected component and a chamber of the valve). For example, a port 70a may be connected to the opening chamber 58, a port 70b may be connected to the low pressure recipient 60, and a port 70c may be connected to the controller 18 (where redundant yellow and blue PODs are typically located). A pressure higher than the hydrostatic pressure may be provided when a fluid communication is enabled between the opening chamber 58 and the controller 18, to provide a force opposite to the force provided when the low pressure recipient 60 is in fluid communication with the opening chamber 58. Thus, the BOP may be closed when the low pressure recipient 60 is in fluid communication with the opening chamber 58, and opened when the controller 18 is in fluid communication with the opening chamber 58. As understood by those of ordinary skill in the art, the closing of the BOPs must be swift (i.e., time and force are of the essence) to prevent damaging of the equipment due to “kicks”, while the opening of the BOPs is less demanding. Thus, providing a higher pressure hydraulic fluid from the surface via the controller 18 may be employed to open the BOPs.
The valve 70 is actuated between the various states by a pilot 80, which can be a mechanic, hydraulic or electro-mechanic mechanism. Once the pilot supply is removed a spring 90 will shift the valve to its normal position. A double piloted valve could also be used to shift the valve from either position if an additional pilot signal was provided.
Cross-sections through a conventional sub plate mounted (SPM) valve 100 (used e.g. in the apparatus 30) are illustrated in FIGS. 5A and 5B. FIG. 6 is a blow-up representation of the parts of the conventional SPM valve 100. As illustrated in FIGS. 5A, 5B and 6, the conventional SPM valve 100 includes an upper seat 101, seals 102a and 102b, a rod seal 103, a backup plate 104, an outer spring 105, an inner spring 106, a spring retainer 107, a split collet 108, a pilot piston 109, a piston seal 110, a piston housing 111, a valve stem 112, a spool 113, a nut 114, a cage 115, a rod seal 116, a seal 117, a lower seat 118 and a valve body 119. The outer spring 105, inner spring 106, spring retainer 107, and split collet 108 are housed within a piston housing chamber 121, which is vented to sea pressure. The conventional SPM valve 100 has a port 130 that can serve to connect to the opening chamber 58, a port 135 that can serve to connect the low pressure vessel 60, and a port 140 that can serve to connect the controller 18. In FIG. 5A, the spool 113 is in a first position being located close to the upper seat 101. In FIG. 5B, the spool 113 is in a second position being located close to the lower seat 118.
This conventional SPM valve 100 is not suitable to be used in the apparatus 50 (i.e., to be connected to a low pressure recipient inside which the pressure may be as low as 1 atm) because it cannot withstand the high pressure difference between the chambers 150, port 135 and chamber 121 of the valve. The upper seat 101 and the backup plate 104 are located at an interface between these chambers. The upper seat 101, which is typically made of plastic is fully supported by backup plate 104 when the valve is exposed to internal pressure in its conventional operating condition. However, when the valve 100 is positioned so that port 130 is aligned with port 135 to align the opening chamber 58 to the low pressure vessel 60, the pressure differential between the seawater pressure in chamber 121 and the low pressure in chamber 150 is felt across upper seat 101. As a result, the plastic seat 101 may deform by bowing outward along valve stem 112 and be prone to damage because it is not fully supported inside port 135 and chamber 150. The plastic seat is used because it is slightly elastic and when the spool 113 comes in contact with the seat 130 the contact surface creates a seal between port 135 and chamber 150 when the spool 113 is engaged on the upper seat 101 and when the valve is operated the opposite contact face of the spool 113 contacts the lower seat 118 and the contact surface creates a seal between chambers 150 and port 140. Also, due to an increased pressure difference inside the valve, the potential of leaking fluid towards the lower pressure chamber foreseeable increases (for example, when a fluid communication between the low pressure recipient 60 and the chamber 150 is established), thereby damaging the valve and the apparatus.
Accordingly, it would be desirable to provide a valve capable to avoid these problems having a sealing system that would make the valve useable undersea, in an arrangement which generates force to operate the BOPs using a low pressure recipient.